I think the honest answer is scalpers/resellers.
While their have been almost no sales for the last few years, the retail price at big-box stores has been more or less stable (10-20% increase at Bass Pro for example). But it’s never in stock. Because even with restriction efforts, plenty of people just buy all that comes in and resell online. And the demand, especially in our currently polarized climate is there.
The manufacturers are reporting being at capacity, as seen here:
In this video, Vanderbrink asks for patience and seeks to quash rumors. While conceding that the pandemic has created challenges, Vanderbrink declares that the ammo plants are running at full capacity:
“We know, ammo seems hard to come by right now. But rest assured, we are building and shipping more and more every day[.] We are making ammunition every minute of every day … We are making more hunting ammo than we ever have. We are doing our damndest to meet the demand!”
And few companies want to invest the $$$ to build new factories with the possibility that by the time construction is done that demand will be back to lower levels, or that the regulatory environment will change. So fixed supply, increased demand, prices keep going up especially with hoarders and scalpers.
Heck, I haven’t gone shooting since 6 months before COVID became a US-wide concern, as prices were already high due to panic buying from social unrest, and it’s only gotten worse. Sure, I could go practice, but I can’t replace what I shoot at any reasonable cost even for common calibers.
For what it’s worth, I’ve seen some online retailers that I trust show prices that while high, aren’t the 200+% markup we had earlier. But even the common calibers are still about 50% higher (and again, with no sales) than 3 years ago.